Liquid jet and recovery system for immersion lithography

ABSTRACT

A liquid immersion lithography apparatus includes a projection system having an optical member of which an incidence side has a convex lens shape, and a flow passage connected to a hole from which liquid is supplied. A substrate is exposed through the liquid covering only a portion of an upper surface of the substrate. The optical member has an end surface via which the exposure light is projected to the substrate via the liquid. A material having the end surface is fused silica.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional of U.S. patent application Ser. No. 15/723,628filed Oct. 3, 2017, which in turn is a Divisional of U.S. patentapplication Ser. No. 15/086,675 filed Mar. 31, 2016 (now U.S. Pat. No.9,785,057), which is a Divisional of U.S. patent application Ser. No.14/283,827 filed May 21, 2014 (now U.S. Pat. No. 9,304,409), which is aDivisional of U.S. patent application Ser. No. 13/200,982 filed Oct. 6,2011 (now abandoned), which is a Divisional of U.S. patent applicationSer. No. 12/232,513 filed Sep. 18, 2008 (now U.S. Pat. No. 8,059,258),which is a Divisional of U.S. patent application Ser. No. 11/236,759filed Sep. 28, 2005 (now U.S. Pat. No. 7,443,482), which is aContinuation of International Application No. PCT/US2004/010071 filedApr. 1, 2004, which claims the benefit of U.S. Provisional PatentApplication No. 60/462,786 filed Apr. 11, 2003. The entire disclosuresof each of the prior applications are hereby incorporated by referencein their entireties.

BACKGROUND

This invention relates to a liquid jet and recovery system for animmersion lithography apparatus, adapted to supply a liquid into thespace between a workpiece such as a wafer and the last-stage opticalelement such as a lens of an optical system for projecting the image ofa reticle onto the workpiece.

Such an immersion lithography system has been disclosed, for example, inW099/49504, which is herein incorporated by reference for describing thegeneral background of the technology and some general considerations.One of the issues with existing immersion lithography mechanisms is thesupplying and recovery of the immersion liquid. An improved system forsupplying and recovering a liquid for immersion lithography is needed.

SUMMARY

Various liquid jet and recovery systems embodying this invention for animmersion lithography apparatus will be described below for having animage pattern projected onto a workpiece such as a wafer. The imagepattern is typically provided by a reticle placed on a reticle stage andprojected by an optical system including an illuminator and a last-stageoptical element that is disposed opposite the workpiece with a gap inbetween that element and the workpiece. The last-stage optical elementmay or may not be a lens and is hereinafter sometimes simply referred toas “the optical element.” The aforementioned gap is hereinafter referredto as “the exposure region” because the image pattern is projected ontothe workpiece through this gap.

The purpose of a liquid jet and recovery system is to supply a fluidsuch as water into this exposure region, to entrain it there at leastduring the projection of the image pattern on the workpiece and toremove (or to recover) it away from the exposure region. In order tocarry out the supply and recovery of the fluid quickly and smoothlywithout generating air bubbles, arrays of nozzles are arranged to havetheir openings located proximal to the exposure region. According to oneaspect of the invention, these nozzles are each adapted to serveselectively either as a source nozzle for supplying a fluid into theexposure region or as a recovery nozzle for recovering the fluid fromthe exposure region. A fluid controlling device is further provided, thefunctions of which include causing nozzles of selected one or more ofthese arrays on one or more of the sides of the exposure region to serveas source nozzles and causing a fluid to be supplied through them intothe exposure region such that the supplied fluid contacts both theworkpiece and the optical element for immersion lithography.

The fluid controlling device also may be adapted to simultaneously causenozzles of selected one or more of the remaining arrays to serve asrecovery nozzles. Since each of the nozzles can serve selectively eitheras a supply nozzle or a recovery nozzle, various flow patterns can berealized by this fluid controlling device. For example, the fluid may besupplied into the exposure region through the nozzles of the array on aspecified side and removed through those on the array on the oppositeside, the nozzles of the arrays on the remaining sides neither supplyingnor recovering the fluid. As another example, the fluid may be suppliedinto the exposure region through the nozzles of mutually oppositelyfacing arrays and recovered through those of the arrays on thetransversely facing arrays. As a third example, a flow in a diagonaldirection may be realized if the fluid is supplied from the nozzles oftwo arrays on mutually adjacent and mutually perpendicular sides of theexposure region and recovered through those of the remaining arrays onthe oppositely facing sides. Alternatively, the fluid may be suppliedthrough all of the nozzles surrounding substantially all around theexposure region to have the fluid entrained inside the exposure region.

According to another aspect of the invention, arrays of nozzlesexclusively adapted to supply a fluid, herein referred to asfluid-supply nozzles, and arrays of nozzles exclusively adapted torecover the fluid, herein referred to as fluid-recovery nozzles, areseparately provided, the fluid-supply nozzles surrounding the exposureregion and the fluid-recovery nozzles surrounding the fluid-supplynozzles from all sides. According to a preferred embodiment, a groove isformed substantially all around the exposure region and thefluid-recovery nozzles are arranged to open into this groove such that auniform flow can be more easily established. In this case too, the fluidcontrolling device can establish the variety of flow patterns asexplained above.

As explained above, the optical element that is disposed opposite theworkpiece and that comes into direct contact with the fluid such aswater need not be a lens. According to a preferred embodiment of theinvention, this last-stage optical element comprises a pair of opticalplates contacting each other across a contact plane and having channelsformed on this contact plane, these channels connecting to the exposureregion such that the fluid can be passed through these channels into orout of the exposure region. This embodiment is preferred because thefluid used for immersion lithography tends to affect the material of theoptical element adversely, and lenses are more expensive and troublesometo replace than optical plates.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in conjunction with the followingdrawings of exemplary embodiments in which like references numeralsdesignate like elements, and in which:

FIG. 1 is a schematic cross-sectional view of an immersion lithographyapparatus that incorporates the invention;

FIG. 2 is a process flow diagram illustrating an exemplary process bywhich semiconductor devices are fabricated using the apparatus shown inFIG. 1 according to the invention;

FIG. 3 is a flowchart of the wafer processing step shown in FIG. 2 inthe case of fabricating semiconductor devices according to theinvention;

FIG. 4 is a schematic plan view of a liquid jet and recovery systemembodying this invention that may be incorporated in the lithographyapparatus of FIG. 1;

FIG. 5 is a schematic side view of the liquid jet and recovery system ofFIG. 4;

FIGS. 6-9 are schematic plan views of the liquid jet and recovery systemof FIGS. 4 and 5 to show various flow patterns that may be established;

FIG. 10 is a schematic plan view of another liquid jet and recoverysystem embodying this invention;

FIG. 11 is a schematic plan view of still another liquid jet andrecovery system embodying this invention;

FIG. 12 is a schematic side view of the liquid jet and recovery systemof FIG. 11;

FIG. 13 is a schematic side view of still another liquid jet andrecovery system embodying this invention; and

FIG. 14 is a schematic plan view of the liquid jet and recovery systemof FIG. 13.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows an immersion lithography apparatus 100 that may incorporatea liquid jet and recovery system embodying this invention, however, thisexemplary example of an immersion lithography apparatus itself is notintended to limit the scope of the invention.

As shown in FIG. 1, the immersion lithography apparatus 100 comprises anilluminator optical unit 1 including a light source such as a KrFexcimer laser unit, an optical integrator (or homogenizer) and a lensand serving to emit pulsed ultraviolet light IL with wavelength 248 nmto be made incident to a pattern on a reticle R. The pattern on thereticle R is projected onto a wafer W coated with a photoresist at aspecified magnification (such as 1/4 or 1/5) through a telecentric lightprojection unit PL. The pulsed light IL may alternatively be ArF excimerlaser light with wavelength 193 nm, F₂ laser light with wavelength 157nm or the i-line of a mercury lamp with wavelength 365 nm. In whatfollows, the coordinate system with X-, Y- and Z-axes as shown in FIG. 1is referenced to explain the directions in describing the structure andfunctions of the lithography apparatus 100. For the convenience ofdisclosure and description, the light projection unit PL is illustratedin FIG. 1 only by way of its last-stage optical element (such as a lens)4 disposed opposite to the wafer W and a cylindrical housing 3containing all the others of its components.

The reticle R is supported on a reticle stage RST incorporating amechanism for moving the reticle R in the X-direction, the Y-directionand the rotary direction around the Z-axis. The two-dimensional positionand orientation of the reticle R on the reticle stage RST are detectedby a laser interferometer (not shown) in real time and the positioningof the reticle R is effected by a main control unit 14 on the basis ofthe detection thus made.

The wafer W is held by a wafer holder (not shown) on a Z-stage 9 forcontrolling the focusing position (along the Z-axis) and the tiltingangle of the wafer W. The Z-stage 9 is affixed to an XY-stage 10 adaptedto move in the XY-plane substantially parallel to the image-formingsurface of the light projection unit PL. The XY-stage 10 is set on abase 11. Thus, the Z-stage 9 serves to match the wafer surface with theimage surface of the light projection unit PL by adjusting the focusingposition (along the Z-axis) and the tilting angle of the wafer W by theauto-focusing and auto-leveling method, and the XY-stage 10 serves toadjust the position of the wafer W in the X-direction and theY-direction.

The two-dimensional position and orientation of the Z-stage 9 (and hencealso of the wafer W) are monitored in real time by another laserinterferometer 13 with reference to a mobile mirror 12 affixed to theZ-stage 9. Control data based on the results of this monitoring aretransmitted from the main control unit 14 to a stage-driving unit 15adapted to control the motions of the Z-stage 9 and the XY-stage 10according to the received control data. At the time of an exposure, theprojection light is made to sequentially move from one to another ofdifferent exposure positions on the wafer W according to the pattern onthe reticle R in a step-and-repeat routine or a step-and-scan routine.

The lithography apparatus 100 being described with reference to FIG. 1is an immersion lithography apparatus and is hence adapted to have aliquid 7 of a specified kind such as water filling the space between thesurface of the wafer W and the lower surface of the last-stage opticalelement 4 of the light projection unit PL at least while the patternimage of the reticle R is being copied onto the wafer W.

The last-stage optical element 4 of the light projection unit PL isdetachably affixed to the cylindrical housing 3. The liquid 7 issupplied from a liquid supply unit 5 that may comprise a tank, apressure pump and a temperature regulator (not individually shown) tothe space above the wafer W under a temperature-regulated condition andis collected by a liquid recovery unit 6. The temperature of the liquid7 is regulated to be approximately the same as the temperature insidethe chamber in which the lithography apparatus 100 itself is disposed.Source nozzles 21 through which the liquid 7 is supplied from the supplyunit 5 and recovery nozzles 23 through which the liquid 7 is collectedinto the recovery unit 6 are only schematically shown. Theirarrangements will be described more in detail below because they areparts of a liquid jet and recovery system to which this inventionrelates.

According to this invention, multiple jets are provided to inject animmersion fluid (referenced above as the liquid 7) between the wafer Wto be exposed and the last-stage optical element 4 of the lightprojection unit PL for projecting an image pattern thereon. FIGS. 4 and5 show schematically the design of a liquid jet and recovery system 200embodying this invention which may be incorporated in the lithographyapparatus 100 described above, FIG. 5 being its horizontal side view andFIG. 4 being its plan view. The design is characterized as having alarge plural number of nozzles 210 arranged in a quasi-continuous mannerin arrays on all sides of the exposure area by the light projection unitPL. According to the embodiment illustrated in FIG. 4, the nozzles 210are arranged in four arrays 211, 212, 213 and 214, each of the arraysbeing on one side of a rectangular formation.

Although FIG. 1 showed the source nozzles 21 connected to the liquidsupply unit 5 and the recovery nozzles 23 connected to the liquidrecovery unit 6 separately, it was for the convenience of illustration.The nozzles 210 shown in FIGS. 4 and 5 instead are each adapted tofunction both as a source nozzle and as a recovery nozzle, or explainedmore precisely, to be controlled so as to function selectively either asa source nozzle or as a recovery nozzle under the control of the maincontrol unit 14.

FIGS. 6-9 show different ways in which the liquid jet and recoverysystem 200 of FIGS. 4 and 5 may be operated. FIG. 6 shows an example inwhich the wafer scan direction is as shown by an arrow and the nozzles210 in one of the arrays (i.e., array 213) are controlled so as tofunction as source nozzles while those in the opposite array 211 arecontrolled so as to function as recovery nozzles, those in the remainingtwo arrays 212 and 214 being controlled to function neither as sourcenozzles nor as recovery nozzles. As a result, the flow pattern of theliquid 7 will be as shown by parallel arrows.

FIG. 7 shows another example in which the nozzles 210 in mutuallyopposite arrays (i.e., arrays 211 and 213) are controlled so as tofunction as source nozzles while those in the remaining arrays 212 and214 are controlled so as to function as recovery nozzles. The resultantflow pattern of the liquid 7 will be as shown by arcuate arrows. Inother words, the wafer W may be moved in two scanning directions whilethe liquid 7 is directed in two orthogonal directions.

FIG. 8 shows still another example in which all nozzles 210 in all ofthe arrays are controlled so as to function as source nozzles, servingto entrain the liquid 7 in the region below the projection lens of thelight projection unit PL between its last-stage optical element 4 andthe wafer W, the flow pattern being shown by radially outwardly pointingarrows.

FIG. 9 shows still another example in which the nozzles 210 in twomutually adjacent arrays (i.e., arrays 211 and 212) are controlled so asto function as source nozzles and those in the remaining arrays 213 and214 are controlled so as to function as recovery nozzles. The resultantflow pattern of the liquid 7 is shown by diagonal arrows.

In summary, in each of these examples, the nozzles 210 are individuallycontrolled, or the jets are connected to valves that can be selectivelyset on and off as source or recovery. They may be arranged such that asingle valve may control several jets together. The jets may beindividual parts or integrated together as a single unit. The valveshown in FIG. 5, therefore, may be regarded as being connected to onlyone nozzle or to a group of nozzles. Alternatively, the nozzles may becontrolled as groups. For example, group 211 may be controlled by asingle valve or groups 211 and 213 may be controlled by a single valve.

FIG. 10 shows another liquid jet and recovery system 220 with analternative arrangement characterized as providing source nozzles 225and recovery nozzles 230 independently. In other words, unlike thesystem 200 shown in FIGS. 4-9 with nozzles each functioning selectivelyeither as a source nozzle or as a recovery nozzle, the system 220 shownin FIG. 10 is provided with the source nozzles 225 which are not adaptedto function as a recovery nozzle and the recovery nozzles 230 which arenot adapted to function as a source nozzle.

According to the example shown in FIG. 10, the source nozzles 225 andthe recovery nozzles 230 are separately arranged in arrays around theexposure area, the arrays of the source nozzles 225 being each arrangedinside the corresponding one of the arrays of the recovery nozzles 230.Each nozzle may be configured with a valve to turn the nozzle on or off.Alternatively, a single valve may control several jets together. Any ofthe flow patterns described above with reference to FIGS. 6-9 can beestablished with the system 220 shown in FIG. 10.

FIGS. 11 and 12 show still another liquid jet and recovery system 240that is similar to the system 220 described above with reference to FIG.10 but is different in that a liquid recovery zone 250 is providedsubstantially all around the exposure area. The liquid recovery zone 250may comprise a channel cut into a supporting port or a loop made of asuitable material. Individually controllable recovery nozzles 230 arelocated in the interior of the recovery zone 250. The zone 250 thusprovided is advantageous in that the liquid 7 can be pumped out moreuniformly. The source nozzles 225 may be independently controlled orused in groups, as in the embodiments explained above, to establish anyof the flow patterns shown in FIGS. 6-9.

In the description given above, the last-stage optical element 4 may ormay not be a lens. The lower surface of this optical element 4, adaptedto come into direct contact with the liquid 7, tends to become soiled asparticles removed from the photoresist and the impurities contained inthe liquid 7 become attached to it. For this reason, the last-stageoptical element 4 may be required to be exchanged from time to time, butif the element that must be replaced by a new element is a lens, themaintenance cost (or the so-called “running cost”) becomesinconveniently high and it takes a longer time for the exchange.

In view of this problem, the light projection unit PL of the immersionlithography apparatus 100 may be designed such that its last-stageoptical element 4 is not a lens. FIGS. 13 and 14 show an exampleembodying this invention characterized as having a pair of mutuallyintimately contacting optical plates (upper plate 41 and lower plate 42)disposed below the lens 40 that would be the last-stage optical element4 of the light projection unit PL but for these plates 41 and 42.

The embodiment of the invention shown in FIGS. 13 and 14 is furthercharacterized as integrating the liquid injection nozzle arrays with thelast-stage optical element of the light projection unit PL. As shown inFIGS. 13 and 14, the lower plate 42 may be provided with grooves on theupper surface so as to form liquid-passing channels 46 as the two plates41 and 42 are attached to each other. The channels 46 each open at thelower surface, and the upper plate 41 is provided with throughholes 47each attached to a hose 48 by way of an adaptor 49 such that the liquid7 may be injected into and recovered from the space between the wafer Wand the lower plate 42 through the channels 46, the throughholes 47 andthe hoses 48.

The optical plates 41 and 42 may be of a known kind having parallelsurfaces serving to correct the optical characteristics of the lightprojection unit PL such as its spherical aberration and coma. Thisembodiment is advantageous because the plates 41 and 42 are lessexpensive to replace than a lens. Substances such as organic siliconcompounds may become attached to the surface of the optical plates 41and 42 so as to adversely affect the optical characteristics of thelight projection unit PL such as its light transmissivity and brightnessas well as the uniformity of brightness on the wafer W but the user hasonly to replace the relatively inexpensive optical plates and therunning cost would be significantly less than if the last-stage opticalelement 4 were a lens. The plates 41 and 42 and the lens 40alternatively may be cemented together by using optical cements suitablefor the wavelengths being used.

The liquid jet and recovery system according to this embodiment isadvantageous for many reasons. First, the nozzles can be set close tothe exposure area. This helps to insure a continuous layer ofbubble-free liquid in the exposure region. It also helps when the edgeof the wafer is being exposed because the edge of the wafer is adiscontinuity and may perturb the liquid layer, causing bubbles to enterthe region being exposed. Second, the layer of liquid around the nozzlesis roughly continuous and uniform, allowing for capillary action to helpmake certain that the liquid layer is uniform. Third, the lens may be ofa material such as calcium fluoride that degrades and dissolves in waterwhile the plates may be a material such as fused silica that is stablein contact with water. Fourth, the region between the channels is openfor auxiliary optical beams. These beams may be used forthrough-the-lens focusing, or for other purposes.

Systems according to this invention are generally capable of providing auniform, bubble-free layer of water between the optical element and thewafer. It may also improve the speed for filling the gap and removingthe liquid in the outward areas of the lens or the stage areassurrounding the wafer. Furthermore, it will prevent degradation of thelens or the surface of the optics that may be affected by the contactwith the immersion fluid.

FIG. 2 is referenced next to describe a process for fabricating asemiconductor device by using an immersion lithography apparatusincorporating a liquid jet and recovery system embodying this invention.In step 301 the device's function and performance characteristics aredesigned. Next, in step 302, a mask (reticle) having a pattern isdesigned according to the previous designing step, and in a parallelstep 303, a wafer is made from a silicon material. The mask patterndesigned in step 302 is exposed onto the wafer from step 303 in step 304by a photolithography system such as the systems described above. Instep 305 the semiconductor device is assembled (including the dicingprocess, bonding process and packaging process), then finally the deviceis inspected in step 306.

FIG. 3 illustrates a detailed flowchart example of the above-mentionedstep 304 in the case of fabricating semiconductor devices. In step 311(oxidation step), the wafer surface is oxidized. In step 312 (CVD step),an insulation film is formed on the wafer surface. In step 313(electrode formation step), electrodes are formed on the wafer by vapordeposition. In step 314 (ion implantation step), ions are implanted inthe wafer. The aforementioned steps 311-314 form the preprocessing stepsfor wafers during wafer processing, and selection is made at each stepaccording to processing requirements.

At each stage of wafer processing, when the above-mentionedpreprocessing steps have been completed, the following post-processingsteps are implemented. During post-processing, initially, in step 315(photoresist formation step), photoresist is applied to a wafer. Next,in step 316 (exposure step), the above-mentioned exposure device is usedto transfer the circuit pattern of a mask (reticle) onto a wafer. Then,in step 317 (developing step), the exposed wafer is developed, and instep 318 (etching step), parts other than residual photoresist (exposedmaterial surface) are removed by etching. In step 319 (photoresistremoval step), unnecessary photoresist remaining after etching isremoved. Multiple circuit patterns are formed by repetition of thesepreprocessing and post-processing steps.

While a lithography system of this invention has been described in termsof several preferred embodiments, there are alterations, permutations,and various equivalents which fall within the scope of this invention.It also should be noted that there are many alternative ways ofimplementing the methods and apparatus of the invention. It also goeswithout saying that the liquid need not be water but may beperfluoropolyether (PFPE) such as Fomblin oil used when the light sourceis F₂ laser (157 nm).

What is claimed is:
 1. A liquid immersion lithography apparatus comprising: a projection system having an optical member of which an incidence side has a convex lens shape; and a flow passage connected to a hole from which liquid is supplied, wherein a substrate is exposed through the liquid covering only a portion of an upper surface of the substrate, the optical member has an end surface via which the exposure light is projected to the substrate via the liquid, and a material having the end surface is fused silica. 